Reproductive functions include control of the menstrual cycle, spermatogenesis, steroidogenesis and lactation, and sex hormone levels have been implicated in breast cancer, cardiovascular disease, osteoporosis, type 2 diabetes and ageing.2, 3, 4, 5 Circulating levels of sex hormones are limited by sex hormone-binding globulin (SHBG), which is a glycoprotein that binds and transports oestradiol, testosterone and dehydroepiandrosterone (DHEA) to a lesser extent.6 Here, SHBG is linked to breast cancer.